1. Field of the Invention
The present invention relates to a solenoid valve of the type comprising a valve body provided with an inlet duct, with an outlet duct and with actuating means designed to selectively bring these two ducts into communication with each other. It applies in particular to the inerting/pressurizing of bottles containing a still liquid, for example a fruit juice, with nitrogen.
2. Description of the Related Art
The technique of inerting/pressurizing containers by means of nitrogen consists in delivering to each container moving on a conveyor, after it has been filled, a predetermined dose of liquid nitrogen. Since the container is open, the onset of vaporization of the nitrogen expels the air in contact with the packaged product and then, after sealing the container, the end of vaporization of the nitrogen puts the container under pressure and stiffens it, thereby making it easier to handle subsequently.
In certain cases, for example when these containers are bottles, it is necessary to inject the required dose of liquid nitrogen into each container, which means using a solenoid valve.
Given the rates at which modern packaging lines run, the response time of the solenoid valve must be of the order of a few milliseconds. In addition, the coil of the solenoid valve must not introduce substantial heat into the liquid nitrogen circuit in order to avoid the formation of gas blockages which would interfere with the discharge of the liquid nitrogen doses.
These conditions are all the more critical as an insufficient dose of liquid nitrogen results in the container being poorly inerted and/or insufficiently pressurized, while an excessive dose runs the risk of causing the container to explode.